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 * Copyright (c) 2004-2022, University of Oslo
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 * may be used to endorse or promote products derived from this software without
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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package org.hisp.dhis.parser.expression.function;

import java.util.Collections;
import java.util.List;
import org.apache.commons.lang3.ArrayUtils;
import org.apache.commons.math3.stat.descriptive.rank.Percentile;
import org.apache.commons.math3.stat.descriptive.rank.Percentile.EstimationType;

/**
 * Vector function: percentile (base class)
 *
 * <p>All percentile functions take two arguments:
 *
 * <p>percentile... ( values, fraction )
 *
 * <p>The percentile is computed according to the EstimationType of the subclass.
 *
 * @author Jim Grace
 */
public abstract class VectorPercentileBase extends VectorFunction<Double> {
  protected VectorPercentileBase() {
    super(Double.class);
  }

  private final Percentile percentile = new Percentile().withEstimationType(getEstimationType());

  @Override
  public Object aggregate(List<Double> values, List<Double> args) {
    Double fraction = args.get(0);

    if (values.size() == 0 || fraction == null || fraction < 0d || fraction > 1d) {
      return null;
    }

    Collections.sort(values);

    if (fraction == 0d) {
      return values.get(0);
    }

    double[] vals = ArrayUtils.toPrimitive(values.toArray(new Double[0]));

    return percentile.evaluate(vals, fraction * 100.);
  }

  /**
   * Each subclass defines its percentile estimation type.
   *
   * @return the percentile estimation type.
   */
  protected abstract EstimationType getEstimationType();
}
